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Windows 7: Windows 7 & 16-bit

To clarify, 16-bit support is not part of Windows x64 because Microsoft wanted to remove it. Its not supported because of hardware constraints. You see, on Windows 16-bit applications are special, require a special mode on the CPU called Legacy Mode. You cannot run a 64-bit OS with Legacy Mode on the processor it has to be in Long Mode. But Long Mode is incompatible with 16-bit Windows applications.

In the end, one is going to have to leave 16-bit behind. Hardware is just going to leave it behind. Soon CPUs won't have a Legacy Mode, thus no more DOS/16-bit Windows applications.

ExDos seems to require a virtual PC in windows 7 64-bit. MS virtual XP is not fully functional on my machine as it seems impossible to use external sound because the virtual soundcard does not have a line-in facility, and does not work reliably with a USB soundcard.

Why would you need ExDos if you had a functioning virtual XP ? That system runs 16-bit applications but is of no use to me because it lacks line-in sound.